Discharge lamp system



Jan. 3, 1939.v M. A. EDWARDS 2,142,837

' DISCHARGE LAMP SYSTEM Filed March 27,` 193'? Figi.

I nverwtor:

S Attorney.

Patented Jan. 3, 19.39 *A l i I' I UNITED STATES PATENT oi-FlcEDISCHARGE LAMP SYSTEM Martin A.Edwards, Schenectady, N. Y., signor ItvoGeerl Electric Company, a corporation of N ew or Application March 27,19,37, Serial No. 133,471

6 Claims. (Cl. 176-124) Myinvention relates to discharge lamp systemsVinserting in the lamp circuit inductive means which operate onalternating current. It is the` which introduces a second harmonic. Inthe object of my invention to provide an improved drawing I have shownsuch inductive means as system of this character whereby the lamp shallcomprising the saturable reactor l having the 6 produce flashes of lighthaving a frequency which' main or alternating current winding 5 included5 is the same as the frequency of the alternating in series with thelamp and the transformer 3 current on which the system operates. andhaving the direct current or saturating wind- Another object of myinvention is the proviing 6 which may be lsupplied by direct currentsion of such a system wherein the maximum` from any suitable source. Itis highly desirable 10 brilliancy of each iiash is high relative to thethat the core of the saturable reactor 4 shall 10 average value of thelight thereof. have a. relatively high permeability. Connected Myinvention will be better understood from in series with the saturatingwinding 6 is the the following description taken in connection reactor ihaving the air gap 8 in its magnetic with the accompanying drawing, andits scope circuit. Forconvenience I have shown the l5 will be pointedout in the appended claims. saturating winding 6 supplied by directcurrent l5 Referring to the drawing, Fig. 1 is a circuit obtainedl fromthe alternating current circuit 2 diagram illustrating an embodiment ofmy inventhrough the full wave rectier 9. However, it tion; Fig. 2 showsthe lamp voltage and current will be understood that any suitable sourceof waves; and Fig.v3 shows the wave of light ilux supply of directcurrent may be employed for of the lamp. this purpose. i 20 In Fig. '1,I have shown the discharge lamp I Referring now to. Fig. 2, let it beassumed that as a gas discharge cold cathode lamp of the during thepositive half cycles ofcurrent in the small high pressure mercury vaportype such as Winding .5 the direction of the current in the thatdisclosed and claimed in the copending apwinding 6 be such as toincrease the ux and l plication of Cornelis Bolet al., Serial No.46,952, cause saturation of the core of the Areactor 4. 25

led October 26, 1935 and assigned to the same The Wave I0 of voltageapplied to the lamp rises assignee as the present application. The lampsuddenly from zero to a point such as Il at which I is shown connectedto be operated from the the lamp breaks dOWn and a discharge takes 60cycle, 110 volt lighting circuit 2. Inasmuch Place therein. The VOItagethereupon diODS t0 a 30 as the lamp requires a higher voltage than thatlower value and continues at a substantially uni- 30 of the circuit 2for its operation, for example, form value through the greater portionof the 440 volts, I have shown it connected with the 'positive halfCycle- The resulting Wave I2 of source of supply through the step-uptranscurrent through the lamp rises rapidly, however, former 3. to amaximum and then decreases to zero caus- It is well known'that when sucha discharge ing the lamp t0 emit a brilliant flash 0f iight. .35

lamp is connected across a source of supply of Upon the fOllOWngnegative half Cycle i3 0f aP- alternating current of proper voltage,there will plied Voltage the COfe Of'the reaCtOr 4 iS 11nbe as manylight flashes as there are alternasaturated and hence the reactor offersa high tions of the current, in other words, the freimpedance t0 the lOW0f Current in the lamp 4o quency of the iight flashes will be equal totwiceu circuit with the result that the voltage applied 4.o

' the frequency of the alternating current. In act0 the lamp isinSuiCieiit t0 Cause the lamp t0 cordance with my invention, now to bedescribed, break d0Wn and t0 emit light- However', the the number ofiiashes produced by the lamp will Voltage during this negative halfCycle iS suf` be one-half the number of alternations, hence cient tomaintain the ionization in the lamp it will equal the frequency oi thealternating produced by the previous half cycle. Hence at 45 current incycles per second. This result I obthe moment that the voltage againbecomes positain by modulating the wave form of the voltage tive thelamp is in condition to break down as supplied to the lamp by inductivemeans whereby soon as the voltage reaches the proper value each halfcycle of supply voltage of one polarity and the above-described processis repeated. causes the lamp to emit light while each half cycleInasmuch as the impedance oii'ered by the rec- 50 of the oppositepolarity does not cause the lamp tier 9 to the ilow of alternatingcurrent induced to produce light but is suiiicient only to maintain inthe saturating winding 6 is extremely small, the ionization in the lampproducedl by the prethereactor l serves to limit both a short circuitvious half cycle. current in the lamp circuit and the peak value Ieffect such modicatlon of the wave form by of the current flow throughthe lamp. Since a 65 discharge in the lamp occurs only during the halfcycles of one polarity, assumed above to be the positive half cycles,there will be only as many light flashes produced by the lamp as thereare half cycles of that polarity. Hence the frequency of the flasheswill equal the frequency of the alternating current supplied to thelamp. This is illustrated graphically by Fig. 3 where the curve I4represents the light ux producedby the lamp, there being one curve offlux for each cycle of applied voltage.

My invention is adapted for various uses. One use, by way of example, isin a motion picture projector wherein the discharge lamp provides thesource of light for the projection. In this case the usual shutter maybe dispensed with provided the number of pictures projected per secondis equal to one-half the frequency of the alternating current supply.For example, if a 60 cycle alternating current is employed the shuttermay be omitted if the intermittent mechanism of the projector isoperated at such a speed or is so constructed that 30 pictures persecond are projected. It is of course necessary to time the lightflashes so that they occur only during those periods in which the filmis stationary` Obviously each picture then will be projected twice, oncefor each flash, the twovprojections serving the same purpose of avoidingthe sensation of icker as does the usual icker shutter.

Another use of my invention is that of a source of illumination fortaking motion pictures. During those periods at which the camera shutteris closed there is no need of having the subject illuminated'or at leastilluminated to the extent necessary for the proper exposure. One maytherefore economize on the production of light by employing a systemsuch as I have disclosed herein and operating the camera shutter insynchronism with the light iiashes. If a 60 cycle current is employedand the camera makes 30 exposures per second the timing of the shuttershould be such that alternate flashes come during `the closed periods ofthe shutter. I prefer, however, in this case to employ a lower frequencycurrent, for example, a current of 24 cycles per second and to operatethe camera at the usual speed to take the standard number or 24 picturesper second. All the light ashes then will be made to occur during theexposure periods of the camera and a maximum economy will be effected.

My invention is particularly well adapted for the above-mentioned usessince by reason of the peaked form of the current curve l2 the lightproduced by the lamp has a high maximum brilliancy, that is, high incomparison with the average value of the light during the flash.

I have chosen the particular embodiment described above as illustrativeof my invention and it will be apparent that various modifications maybe made without departing from the spirit and scope of my inventionwhich modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1.` In combination, an electric discharge lamp, a saturable reactorhaving a main and a saturating winding, means for connecting said lampand said main winding in series with a source of alternating currentsupply and means having inductive reactance for supplying direct currentto said saturating winding.

2. In combination, an electric discharge lamp, means for supplyingalternating current thereto and al reactor in circuit with said lamphaving means for producing a unidirectional flux therein to causesaturation therein at alternate half cycles of the supplied current.

3. In combination, an electric discharge lamp, a source of supply ofalternating current connected therewith and inductive means in circuitwith the lamp for reducing the amplitude of the half cycles of onepolarity with respect to those of the other polarity whereby alternatehalf cyclesproduce discharges in the lamp and the other half cycles arelimited in amplitude to that required to maintain ionization in thelamp.

4. A system arranged to be energized by alternating current forproducing light ashes having a frequency equal to the frequency of saidalternating current comprising a source of alternating current supply, astepup transformer having its primary connected therewith, an electricdischarge lamp connected with the secondary of said transformer, asaturable core reactor having a main winding connected in series withsaid lamp and secondary and having a saturating winding, and meansincluding a reactor for supplying direct current to said saturatingwinding.

5. In combination, an electric discharge lamp, means for supplyingalternating current thereto and a saturated core reactor in circuit withsaid lamp for causing the frequency of the lamp flashes to equal thefrequency of said current.

6. In combination, an electric discharge lamp, means for supplyingalternating current thereto and inductive means in circuit with saidlamp providing a higher impedance during the half cycles of one polaritythan during the half cycles of the opposite polarity for limiting theflashes oi' said lamp to each alternate half cycle of saidi current.

' MARTIN A. EDWARDS.

